From what I understand generally Coke is carbonated to roughly 6.2 g per liter in bottles and cans, or 3.1 volumes of CO2. I was watching this video because I was curious about how fountain soda machines worked.


By the end of the video they suggest that the soda is carbonated to around 5 volumes of carbonation. Which as I understand would be somewhere in the realm of 11 g of CO2 per liter, almost twice that of the normal soda. I imagine there are a couple other factors involved, like they are dispensing more CO2 than is actually dissolved in the soda as a consequence of trying to instantly carbonate. According to everything I know about carbonation I know from beer making they are carbonating almost 20 times higher than a forced beer carbonation technique in home brewing. Can anyone help me better understand this? I would think that the carbonation level difference between bottled and fountain soda would be something highly controlled by beverage companies for the sake of product consistency.

I did some additional reading and found that the correct maintenance levels on soda fountains with chilled water to roughly 40 degrees F is 75 psi if that helps. For 3.1 volumes of carbonation as I understand equilibrium would be just like 5 psig. I know I missing something big.

I can only assume that the rate of carbonation loss is inversely exponential as the carbonation approaches closer to equilibrium for the environmental pressure. Would 5 volumes rapidly decarbonate to 2-3 volumes but not get much lower very quickly?


If the soda is not distributed, the rate of loss of $\ce{CO2}$ would be an exponential decay. So changing from 5 volumes to 3 volumes is faster than from 3 to 1 volumes.

A can of soda with 3 volumes of $\ce{CO2}$ has about 15 psi of extra pressure inside the can. If it was increased to 25 psi (5 volumes, like the fountain sodas), the can would need to be thicker to ensure it doesn't rupture, which would increase the cost of the can. There is a balance of the amount of $\ce{CO2}$ and the cost for the drink.

  • $\begingroup$ this is in reference to fountain soda though, not canned soda, and the pressure of co2 in fountain soda machines is 76-105 psi, and the discovery channel video suggests its dispensed at 5 volumes. so im confused. $\endgroup$ – user6794 Jun 10 '14 at 3:59
  • $\begingroup$ @user6794 Which do you think tastes better, can sodas or fountain sodas? I prefer fountain sodas. If the formula is the same for fountain and can sodas, the only difference is in the amount of $CO_2$. I was explaining why they don't have more $CO_2$ in can drinks. $\endgroup$ – LDC3 Jun 10 '14 at 4:09
  • $\begingroup$ Thats my question tho, what is the carbonation level of fountain drinks. $\endgroup$ – user6794 Jun 10 '14 at 4:10
  • $\begingroup$ @user6794 Didn't the video say it was 5 volumes. I know can sodas are about 3 volumes. $\endgroup$ – LDC3 Jun 10 '14 at 4:13
  • 1
    $\begingroup$ @user6794 Dispensing a fountain drink with 5 volumes may drop it down to 3 volumes. Opening a can with 3 volumes may drop it to 2.5 volumes. Pouring it out of the can may drop it below 2 volumes. I would say that you will always have more $\ce{CO2}$ from a fountain drink than from a can (with the same time from dispensing it). $\endgroup$ – LDC3 Jun 10 '14 at 4:22

The fountains over carbonate because the beverage is open for possibly a long time before being enjoyed and the idea is to have a happy customer. It is chilled but warming and approaching equilibrium with air (close to 0% CO2) as the dispensing ends.

A lot of the CO2 is already leaving at the time of dispensing which causes agitation and assists in the final mixing of the syrup. They have to operate at high pressures to achieve the high carbonation prior to dispensing in a continuous process with low dwell time for the gas and water.

Those who drink beer often are displeased with bubbles, they prefer the product to hold a stable head of foam rather than have continuously rising bubbles, using CO2 concentrations as provided by a soda fountain would cause pretty much any beer product to foam out of the cup as the bubbles will be too large and numerous.


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